As the dimensions of trench-based transistors shrink, the influence of the highly-doped source/body contact on the net body doping near the channel region becomes more important. For wider lateral distribution of the source/body contact diffusion with 2-3 orders of magnitude higher doping levels compared to the body doping, Vth (threshold voltage) and RonA (on-state resistance) of the device increases. Increasing the distance between the source/body contact and the channel region causes depletion of the body at high drain voltages which can lead to high DIBL (drain-induced barrier lowering). Furthermore, the process window variation for both trench width and contact width as well as contact misalignment must become smaller to avoid these adverse effects (higher Vth, higher RonA and higher DIBL).
Hence, better control of the lateral out-diffusion of the source/body contact doping is desirable.